US2143915A

US2143915A - Indirectly heated cathode

Info

Publication number: US2143915A
Application number: US109621A
Authority: US
Inventors: Jobst Gunther
Original assignee: Telefunken AG
Current assignee: Telefunken AG
Priority date: 1935-11-07
Filing date: 1936-11-07
Publication date: 1939-01-17
Anticipated expiration: 1956-01-17

Description

Jan. 17, 1939. G. JOBST INDIRECTLY HEATED CATHODE Filed Nov. '7, 1936 w mo J R E m NN IE ATTORNEY Patented Jan. 17, 1939 UNITED STATES PATENT OFFICE INDIRECTLY HEATED CATHODE raphic in. b. H., Berlin,

tion of Germany Germany, a corpora- Application November 7, 1936, Serial No. 109,621 In Germany November 7, 1935 4 Claims.

In indirectly heated cathodes the flow of heat from the filament to the surface of the cathode causes a temperature gradient from the heating Wire to the outer shell which is greater the larger the required heat input and the poorer the heat transfer from the source of heat to the surface. High temperatures in the interior or" the cathode entails a number of disadvantages, such as disintegration of the insulation and heating Wire material.

The present invention avoids these difiiculties by reducing the temperature difference between the heater and exterior of the cathode with its electron emissive coating by a good heat conducting medium such as a metal intermediate wall in good heat conducting relation with the heating Wire and with the cathode cylinder or sleeve. The metal intermediate Wall may act as a rigid support for the hot filament.

According to the present invention, the insulating layer electrically separating the heating Wire from the metal intermediate Wall is made as thin as feasible to insure proper electrical insulation and good heat conduction between the wire and the Wall. It is known that the insulating property of most insulators is better at lower temperatures. The heating wire may be coated with insulating material and supported on the intermediate Wall or upon supplementary supporting means. To dispose greater lengths of heating Wire in the cathode it is preferable to provide a meander-formed arrangement of the insulated heating wire on the intermediate Wall. The cathode may be elliptical in cross-section on the major axis of which is placed the intermediate wall.

The intermediate Wall may be curved at its .edge, and the curved portion of the Wall held in good heat conducting contact with the inside surface of the cathode sleeve. A supporting and centering pin for the cathode assembly may be attached to the intermediate wall. The temperature distribution throughout the length of the cathode may readily be controlled by properly arranging the heater Wire on the intermediate wall.

The characteristic features of this invention are set forth in the appended claims and preferred embodiments thereof and are described in the following specification and shown in the accompanying drawing in which:

Figure 1 is a cross-sectional View of a core assembly ready for insertion in a cathode sleeve;

Figure 2 is a perspective view of an assembled intermediate wall and heating wire constructed in accordance with this invention;

Figure 3 is a cross-sectional view of another cathode core constructed in accordance with this invention;

Figures 4 and 5 are perspective views of another intermediate wall and heater wire assembly of this invention; and

Figure 6 is a perspective View of an electrode mount showing fragmentarily the novel cathode core assembly of this invention secured in its proper spaced relation to the other electrodes.

The core assembly shown in transverse crosssection in Figure 1 without the cathode sleeve, comprise heating wires H enclosed by an insulating coating or layer S1 and bearing against the intermediate Wall W, the edges of which are curved on a radius equal to the radius of the inside of the cathode sleeve. A second insulation S2 is filled into the space defined by the wall, its outer surface being rounded on the same radius as the edge portion of the wall. The assembly of Figure 1 may be inserted in a cathode sleeve with the wall edges in good heat conducting contact With the sleeve. The intermediate wall and the bent edges mechanically stiffen the core assembly and protect the insulation during manufacture.

Figure 2 shows the intermediate or separating wall in perspective with insulated heating wire H disposed on the wall and stretched lengthwise of the wall in several V formations. Insulation S2 has been omitted in this figure for the sake of clarity.

Figure 3 shows a core elliptical in cross-section with a surrounding shell or sleeve N exteriorly sensitized with an electron emitting coating and Which bears snugly against the bent portions of separating wall W and the insulating filler S2 of the core. In this embodiment of the invention the heating wire H, as shown in Figure 4, is laid meander-like against the wall W. The wall W at those portions of its surfaces that face the heating wire is insulated by layers S3.

In Figure 5 insulated heating wire is wound bifilar on the metallic plate of the separating wall W and is held at the edges of the plate in notches V. The sides of the wall may be insulated if desired, and the core assembly may be filled and rounded out with insulation for easy insertion in cathode sleeve N.

Figure 6 shows means for supporting the heating element in an electrode assembly and, for convenience of illustration, the filler for the core and theouter shell and the grid of the tube have been omitted. The cathode core assembly is supported at its lower end by wire D embedded in the press and fastened to the intermediate wall and at the upper end by a guiding pin F in an insulating strip G such as of mica that is supported by anode stays A.

I claim:

1. An indirectly heated cathode for electron tubes comprising a cylindrical metal sleeve exteriorly sensitized with an electron emissive coating, an insulated heater wire in said sleeve extending throughout the length of the sleeve, and means for efficiently conducting heat from said wire radially outward to the Wall of said sleeve comprising a metal wall of good heat conductivity in the sleeve and extending across the sleeve throughout the length of the sleeve and good,

thermal contact with the insulated wire and with the interior and intermediate the ends of the sleeve.

-2.,An' indirectly heated cathode for electron tubes comprising a thintwalledcylindrical sleeve exteriorly sensitized with, electron emisssive, substance, a heating assembly in said sleeve comprising a heater wire and a metal wall, of. goodv heat conductivity, said;wall being in good: thermal contact with the interior of the sleeve at spaced points throughout the length of the sleeve, and the wall being covered with insulating material and the heating wire supported in grooves in the insulated wall.

3. An indirectly heated cathode for electron tubes comprising a thin wall cylindrical sleeve exteriorly sensitized with electron emissive substance, a heating assembly in said sleeve comprising an insulated heater, wire and a metal wall of good heat conductivity, said wall being bent at its edge on a curvature the same as the curvature of the inner surface of said sleeve and in good heat conducting contact with the sleeve, said wall being in good thermal contact with said insulated heater wire.

4. An indirectly heated cathode for electron tubes comprising a thin walled cylindrical sleeve exteriorly sensitized with electron emissive substance, aheating asembly within said sleeve comprising an, insulating heater wire and a metal Wall of good heat conductivity, said wall extending' across the interior of the sleeve and being in ood thermal contact with said insulated heater Wire and in, contact with the sleeve substantially throughout its length to provide a uniform temperature distribution along said thin walled sleeve.

GUNTI-IER JOBST.